Rinse and sort cranberries, removing any that look soft or spoiled.

In a saucepan, combine cranberries, water, and 6 tablespoons sugar. Bring to a boil over medium-high heat.

Reduce to medium-low, cover with a splatter screen, and simmer 10–15 minutes, stirring often, until berries break down. Cool 30 minutes.

Preheat oven to 325°F. Line a 9-inch square pan with parchment, leaving overhang for lifting. Grease lightly.

Mix melted butter, sugar, vanilla, and salt in a bowl. Add flour and stir until a dough forms.

Press dough evenly into the pan. Bake 16–18 minutes until lightly golden. Remove and poke holes with a fork. Cool 20 minutes.

In a bowl, whisk sugar and flour. Add eggs, then lemon juice, whisking until smooth.

Spread cooled cranberry filling over crust and chill 45 minutes.

Preheat oven to 350°F. Pour lemon mixture over cranberry layer.

Bake 43–45 minutes, or until center is set and no longer jiggles.

Cool 1 hour at room temperature, then chill 1–2 hours.

Lift out of the pan, dust with powdered sugar, and slice into squares. Wipe knife between cuts.